Comparison of image quality in computed laminography and tomography

In computed tomography (CT), projection images of the sample are acquired over an angular range between 180 to 360 degrees around a rotation axis. A special case of CT is that of limited-angle CT, where some of the rotation angles are inaccessible, leading to artefacts in the reconstrucion because of missing information. The case of flat samples is considered, where the projection angles that are close to the sample surface are either i) completely unavailable or ii) very noisy due to the limited transmission at these angles. Computed laminography (CL) is an imaging technique especially suited for flat samples. CL is a generalization of CT that uses a rotation axis tilted by less than 90 degrees with respect to the incident beam. Thus CL avoids using projections from angles closest to the sample surface. We make a quantitative comparison of the imaging artefacts between CL and limited-angle CT for the case of a parallel-beam geometry. Both experimental and simulated images are used to characterize the effect of the artefacts on the resolution and visible image features. The results indicate that CL has an advantage over CT in cases when the missing angular range is a significant portion of the total angular range. In the case when the quality of the projections is limited by noise, CT allows a better tradeoff between the noise level and the missing angular range.